1. Field of the Invention
The present invention relates to a pigment ink, an ink set, an ink jet recording method, an ink cartridge, a recording unit, an ink jet recording apparatus, and an image forming method.
2. Description of the Related Art
An ink jet recording method is a method of recording an image involving ejecting ink onto a recording medium, and does not require a complicated apparatus, and hence a running cost can be suppressed to a low level, and, for example, a reduction in size of an ink jet recording apparatus and the colorization of images formed by the apparatus can be easily performed. Accordingly, various recording apparatuses employing the ink jet recording method, such as a printer, a copying machine, a facsimile, and a word processor, have been in widespread use.
In such an ink jet recording technique, plural color images are formed by using a black ink and color inks (such as a yellow ink, a cyan ink, a magenta ink, a red ink, a green ink, and a blue ink). An ink containing a pigment as a coloring material has been used as the black ink among those inks for the purpose of, for example, providing an excellent image density and excellent letter quality (see Japanese Patent Application Laid-Open No. 2000-198955).
When plural inks having different hues are applied to a recording medium so as to be adjacent to each other in the ink jet recording method, there is a problem in that a phenomenon (bleeding) occurs in which the plural inks having different hues mix with each other at boundary portions between images formed from the inks. In particular, the occurrence of bleeding at a boundary portion between images formed by a black ink and a color ink has a great influence on deterioration in image quality. In view of the foregoing, various techniques have been developed for obtaining excellent bleeding resistance.
A representative method of solving the problem involves inducing thickening, or agglomeration or precipitation of a coloring material, to at least one type of ink when plural inks having different hues are applied to a recording medium so as to be adjacent to each other, thereby suppressing the occurrence of bleeding. For example, a method is disclosed in which either an anionic ink or a cationic ink is made up to contain a polymer having the same ionicity as the ink, and these inks are applied to a recording medium to come in contact with each other (see Japanese Patent No. 2889817). In addition, a method is disclosed involving applying to a recording medium a first ink and a second ink containing a precipitant that reacts with a coloring material in the first ink to produce precipitate so that the inks are brought into contact with each other (see Japanese Patent No. 3538209). In addition, a polyvalent metal is used as the precipitant.
In recent years, the reliability of the prevention of ink clogging or the stable performance of ink ejection has been requested at a higher level. For example, there is a proposal concerning the prevention of ink clogging caused by agglomerate adhering to a surface having an ejection orifice of a recording head or agglomeration of components in the ink at the time of wiping, when a reactive ink is used. For example, it is disclosed that when recording is performed by using a recording head in which one orifice plate is provided with ejection orifices for plural inks that react with each other, agglomerate produced by a reaction between the inks can be redissolved or redispersed in any one of the inks (see Japanese Patent Application Laid-Open No. 2005-161842).
However, with ink jet recording apparatuses using ink, none of the above-mentioned techniques could sufficiently achieve a high level of reliability that has been requested in recent years.
Further, it has been performed that ink concentrated by evaporation, or agglomerate present near an ink ejection orifice is removed by a sucking operation by using a cap having a sucking mechanism in order that the ink ejection orifice may be capped.
Such techniques for obtaining excellent bleeding resistance as described above have improved image quality. However, in conventional techniques, emphasis has been placed on an efficient reaction between inks, that is, how to improve reactivity between inks for obtaining excellent bleeding resistance, hence sufficient reliability could not be obtained in some cases. In view of the foregoing, in order to solve the problem as described above, the capping of ejection orifices for ejecting plural inks that react with each other with plural caps has been widely performed. However, the use of such plural caps as described above results in an increase in size of an ink jet recording apparatus, the complication of the mechanism of the apparatus and an increase in cost.
In view of the foregoing, the inventors of the present invention have conducted investigation with a view to achieving the acquisition of reliability, a reduction in size of an ink jet recording apparatus and the simplification of the mechanism of the apparatus, and a reduction in cost simultaneously. That is, the inventors have made an investigation into the capping of ejection orifices for a pigment ink and ejection orifices for an ink that reacts with the pigment ink with the identical cap (cap exclusively used when being left standing). As a result, the inventors have found that the above-mentioned constitution, that is, the mere capping of ejection orifices for plural inks that react with each other with the identical cap cannot sufficiently provide a high level of reliability that has been requested in recent years. Further, the inventors have found that other means may be necessary for sufficiently obtaining reliability, and a reduction in size of an ink jet recording apparatus, the simplification of the mechanism of the apparatus, and a reduction in cost cannot be achieved without the means.
The inventors of the present invention have conducted research on the capping of ejection orifices for plural inks that react with each other with one cap having a sucking mechanism disclosed in Japanese Patent Nos. 2889817 and 3538209, and Japanese Patent Application Laid-Open No. 2005-161842. As a result, the inventors of the present invention have found that when performing a sucking operation, the plural inks that react with each other come in contact with each other to produce agglomerate, and the agglomerate adheres to a recording head, with the result that reliability deteriorates.
Therefore, the first object of the present invention is to provide a pigment ink for use in an ink jet recording apparatus in which an ejection orifice for the pigment ink and an ejection orifice for an ink that reacts with the pigment ink are capped with the same cap, the pigment ink achieving the compatibility between bleeding resistance and reliability.
Further, the second object of the present invention is, in addition to attaining the above-mentioned first object of the present invention, to provide a pigment ink capable of providing excellent image quality.
In recent years, in an ink jet recording method, in order that additionally excellent image quality may be obtained, a method has been performed in which an image having a width equal to the length of a recording head is scanned twice or more with a recording head in the main scanning direction in a bi-directional manner to be recorded (hereinafter referred to as “multi-pass recording”). However, when the multi-pass recording is performed, increasing the number of nozzles, or lengthening the recording head may be unable to shorten a recording time sufficiently. In view of the foregoing, a method of performing recording in both the forward and backward directions of main scanning (hereinafter referred to as “bi-directional recording”), or a method of recording an image having a width equal to the length of a recording head by one main scanning (hereinafter referred to as “one-pass recording”) has been attempted to shorten a recording time. When performing recording by combining the one-pass recording and the bi-directional recording, i.e., performing one-pass, bi-directional recording, there is no need to scan multiple times one site on a recording medium, and a recording time can be largely shortened. However, as a result of the investigation conducted by the inventors of the present invention, it has been found that performing recording at a high speed as in the case of the one-pass, bi-directional recording involves the remarkable occurrence of bi-directional unevenness when a pigment ink and an ink that reacts with the pigment ink are applied to a recording medium so as to overlap each other.
Therefore, the third object of the present invention is, in addition to attain the above-mentioned first and second objects of the present invention, to provide a pigment ink capable of suppressing the occurrence of bi-directional unevenness in image formation by bi-directional recording.
In addition, another object of the present invention is to provide an ink set, an ink jet recording method, an ink cartridge, a recording unit, an ink jet recording apparatus and an image forming method which use the above pigment ink.